Following a scuffle with the Turtles, the three of them, who were used as genetic experiments by Foot Technicians, befriended the Turtles. Along with his mutated companions, he traveled in the direction of an underground city, and was captured by a mysterious Entity. The Turtles were able to release him and the other captives. By then, the underground city's crystal moon had returned him to his human state, but it was soon found that removing them from the crystal moon's presence caused an immediate reversion back to mutant form. All the afflicted mutants were forced to stay underground until Donatello could formulate a cure.
However, the mutated humans became impatient and attempted their own experiments, which included trying to break a piece of the crystal moon from the cave ceiling. This caused the moon to fall into a lake of lava, and the immediate reversion of all the people in the city. Razorfist became a mad, mindless mutant once again, until Quarry and Donatello were able to raise the crystal moon from the lava again.
Along with everyone else in the city, he was given the injection that permanently restored him to human form, and was brought back to the surface.